In the formation of seam welded tubing, a seam guide, as taught by Crawford in U.S. Pat. No. 2,936,357 and Hellman, Sr. in U.S. Pat. No. 4,905,885, is used to align the seam to be welded with the welder. However, due to imperfections in the metal strip, the formation of the seam by the preceding forming rolls will not be aligned with the seam guide. As a result, one edge or the other of the seam being formed may engage the edge of the seam guide with enough force to cause that edge to be galled or otherwise deformed and fail to maintain alignment under the welder. This deformation of an edge of the metal strip often results in defects in the welded seam and the misalignment can cause the strip edges to be welded out of registry. As a result, the tube forming process must be closely monitored and the tube fabrication process be stopped when a twist in the seam being formed is detected.
Attempts to solve this problem are taught by Crawford in U.S. Pat. No. 2,936,357, Kato et al, U.S. Pat. No. 4,299,708 and by Nakako in Japanese Application 99224. All three disclose a rolling seam guide in the form of an annular fin. Kato et al. and Nakako teach that the annular fin is provided on the internal surface of one or more of roll just prior to welding. These rolls serve as tube forming rolls and seam guides.
Although these rolling seam guides reduce the galling and deformation of the edges forming the seam, problems are still encountered. The invention is a mechanism for removing the twist in the metal strip as it is being shaped into a tubular form which substantially eliminates the galling and deformation of the edges as they are being guided by the seam guide and effectively assures that the edges of the metal strip are not misaligned when welded.